Hibernate | ManyToOne relation fetchs object once

Question

I have 2 entities, User and Post. Using spring-boot

Users have many posts and Posts have one user. I annotated them as shown below. When I make an request for all posts in DB, It returns a list for Posts like below.

POST 1 and POST 2 have same User property and only one of them can fetch related User. When another Post has another different User for the first time, it can fetch that User.

I need full User object for each Post entry.

(I use Lombok [@Data])

Result (json)

[{
    "id": 1,
    "context": "POST 1",
    "user": {
        "id": 1,
        "username": "user_1",
        "picture": "pic_1",
        "is_active": true,
        "is_verified": true
    }
},
{
    "id": 2,
    "context": "POST 2",
    "user": 1,
},
{
    "id": 3,
    "context": "POST 3",
    "user": {
        "id": 2,
        "username": "user_2",
        "picture": "pic_2",
        "is_active": true,
        "is_verified": true
    }
}]

Post.java

@Data
@Entity(name = "Post")
@Table(name = "post")
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public class Post extends PersistentObject implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String context;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    @JsonIgnoreProperties(ignoreUnknown = true, value = {"password", "isActive", "isVerified", "blockedUsers"})
    private User user;
}

User.java

@Data
    @Entity(name = "User")
    @Table(name = "user")
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler", "posts", "following_locations", "blocked_users"})
@DynamicUpdate
public class User extends PersistentObject implements Serializable
{

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @JsonProperty("username")
    private String username;

    @JsonProperty("password")
    private String password;

    @JsonProperty("picture")
    private String picture;

    @JsonProperty("is_active")
    private Boolean isActive;

    @JsonProperty("is_verified")
    private Boolean isVerified;

    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
    @JsonBackReference(value = "user_posts")
    @JsonProperty("posts")
    private List<Post> posts;

    @OneToMany(mappedBy = "id", fetch = FetchType.LAZY)
    @JsonBackReference(value = "user_following_locations")
    @JsonProperty("following_locations")
    public List<Location> followingLocations;

    @OneToMany(mappedBy = "blocker", fetch = FetchType.LAZY)
    @JsonProperty("blocked_users")
    private List<BlockedUser> blockedUsers;
}

I need full User Object for each Post entry. But I get only once for each user and when another post contains same user again it's only user id, not the User Object — Mahir Köle, Mar 03 '19 at 15:08
This well know problem. See [Jackson: @JsonIdentityInfo Object instead of id](https://stackoverflow.com/questions/34568490/jackson-jsonidentityinfo-object-instead-of-id) and [deserialize Jackson object in JavaScript containing JsonIdentityInfo](https://stackoverflow.com/questions/24208167/deserialize-jackson-object-in-javascript-containing-jsonidentityinfo) — Michał Ziober, Mar 03 '19 at 18:26
Thank you Michal, it solved my problem. @JsonIdentityInfo is the cause to one-time serialization for objects. — Mahir Köle, Mar 11 '19 at 19:59

score 0 · Accepted Answer · answered Mar 11 '19 at 20:02

0

As Michal Ziober mentioned above, It was because of @JsonIdentityInfo annotation. It makes objects get serialized one-time.

answered Mar 11 '19 at 20:02

Mahir Köle

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Hibernate | ManyToOne relation fetchs object once

Result (json)

Post.java

User.java

1 Answers1